This invention relates to a printer control apparatus for controlling an ink-jet printer, for example.
A general ink-jet printer performs printing with a print head which is relatively moved with respect to printing paper. Jpn. Pat. Appln. KOKAI Publication No. 7-266580 discloses an ink-jet printer which performs printing by use of an ink-jet print head 2 disposed to face printing paper wound around a rotary drum 1 as shown in FIG. 34. The rotary drum 1 is rotated by a motor 3 and rotation of the rotary drum 1 is detected by an encoder 4. A motor 5 rotates a rotating shaft 6 disposed in parallel to the rotary drum 1 so as to move a fixed table 7 having the print head 2 mounted thereon in parallel to the rotary drum 1. Specifically, if the rotary drum 1 is rotated by the motor 3, the encoder 4 detects the rotation of the drum 1 to output a signal at each preset pitch and a CPU 8 receives the signal to drive a driver 9 which in turn drives the print head 2 in synchronism with the signal. Further, the CPU 8 drives the motor 5 in synchronism with the rotation of the rotary drum 1 to move the print head 2 by a preset amount. Thus, printing is done on printing paper wound around the rotary drum 1.
Further, in Jpn. Pat. Appln. KOKAI Publication No. 8-156328, as shown in FIG. 35, a print head 13 mounted on a carrier 12 is disposed to face a platen 11 and the carrier 12 is fixed on a carrier belt 16 which is stretched between the rotating shaft of a carrier motor 14 disposed on one side in the main scanning direction and the encoder shaft of a slit disk 15 of a 2-phase encoder disposed on the other side. The carrier belt 16 is driven by rotation of the carrier motor 14 to control and move the carrier 12 along a shaft 17 in the main scanning direction. The slit disk 15 is rotated by driving the carrier belt 16 and passage of each slit of the slit disk 15 is detected by an encoder sensor 18, and phase "A " and phase "B" outputs are generated as shown in FIG. 36.
The relative movement between the print head and the recording medium is generally attained at a constant speed by use of the motor, and during the relative movement, dots are printed on the recording medium at regular intervals by driving the print head in a preset cycle. The dot pitch is expressed by the unit of dpi (dot/inch) and is generally set to approx. 300 dpi to 1200 dpi.
The printing precision is primarily reduced by a degradation in the constant velocity of the relative movement. Therefore, the encoder is provided to detect the position of the drum which is required for a rotation and movement control. For example, in the case of FIG. 34, rotation of the rotary drum 1 is detected by the encoder 4 and the CPU 8 feedback-controls the speed of the motor 3 to make the time interval corresponding to the detected value constant.
However, in the above method, there is a limitation in the printing precision. One of the reasons is that delay time occurs in the feedback control without fail and it takes a long time until the variation is suppressed. Another reason is that the gain of the feedback loop cannot be made excessively large because of the delay time.
In the case of FIG. 35, the movement of the carrier 12 is detected when the encoder sensor 18 detects passage of each slit of the slit disk 15 rotated by driving the carrier belt 16 and a print timing pulse for starting the driving of the print head 13 is created according to the result of detection. The print head 13 can be driven to follow the movement of the carrier 12 by driving the print head 13 at the timing of the print timing pulse.
Further, in Jpn. Pat. Appln. KOKAI Publication No. 8-156328, an attempt is made to enhance the printing resolution. That is, as shown in FIG. 37, an up-counter 19 and down-counter 20 are provided, a Load 1 signal is derived from the phase "A" output ((a) in FIG. 38) from the encoder sensor 18 as shown in (c) of FIG. 38 and the Load 1 signal is input to the Load terminal of the up-counter 19. The up-counter 19 counts the pulse interval of the Load 1 signal by use of a clock CLK and the down-counter 20 is loaded with a value which is half the maximum count of the up-counter 19 by a Load 2 signal shown in (e) of FIG. 38 and counts the same. Therefore, a timing pulse is output from the down-counter 20 at a timing which is half the period of the Load 1 signal. The timing signal and a signal obtained by inverting the Load 1 signal by an inverter 21 are input to an OR gate 22 so as to output a print timing signal as shown in (d) of FIG. 38 with the resolution which is twice the resolution of the encoder.
Thus, the ink-jet printer disclosed in Jpn. Pat. Appln. KOKAI Publication No. 8-156328 has an advantage that it can cope with the high resolution.
However, the ink-jet printer disclosed in Jpn. Pat. Appln. KOKAI Publication No. 8-156328 is effective in a case where the Load 1 signal, that is, a reference point pulse is halved to create a print timing signal and the number of divisions is small, but a problem occurs when the number of divisions is increased to further enhance the resolution.
For example, assume a case wherein an interval of reference point pulses is divided into six portions. As shown in FIG. 39, when the reference point pulses are changed to have intervals a1, a2, a3, a4, a5, the print timing pulses are obtained as a combination of pulses of a period which is 1/6 of each of a1 to a5 and the original reference point pulses so that a difference between the intervals of the reference point pulses will be concentrated on the last one of the six-divided periods. That is, when the print timing pulses are created based on the interval a1 of the reference point pulses, the interval a1 is divided into six portions, but since the period used when printing is actually done is the interval a2 which appears one period after the interval a1, the first to fifth print timing pulses are created based on the contents of the divisions, but the sixth print timing pulse is created based on the reference point pulse and the last pulse interval of the print timing pulses becomes shorter if the interval a2 is shorter than the interval a1. If the time width of the pulse interval becomes shorter than the response time of the print head, there occurs a problem that printing will not be done.
Therefore, as shown in FIG. 40, if the next reference point pulse is not used to create the sixth print timing pulse and this print timing pulse is created at a timing obtained by dividing the interval a1 into six portions, the first interval of the print timing pulses of the next period becomes shorter, thereby causing the same problem.
Thus, in the prior art, in a case where the print control is effected by detecting the relative position between the print head and the recording medium by use of the encoder, there occurs a problem that printing cannot be done if the number of divisions of the reference point pulse interval is increased to enhance the printing precision.